Solar cell and method for manufacturing the same

ABSTRACT

A solar cell and a method for manufacturing the same are discussed. The solar cell includes a substrate containing impurities of a first conductive type, an emitter region which is positioned at a front surface of the substrate and contains impurities of a second conductive type opposite the first conductive type, a back passivation layer which is positioned on a back surface of the substrate and has openings, a back surface field region containing impurities of the first conductive type, a first electrode connected to the emitter region, and a second electrode connected to the back surface field region. The back surface field region includes a first back surface field region positioned on the back passivation layer and a second back surface field region, which is positioned at the back surface of the substrate exposed by the openings of the back passivation layer.

This application claims priority to and the benefit of Korean PatentApplication No. 10-2013-0006410 filed in the Korean IntellectualProperly Office on Jan. 21, 2013, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention relate to a solar cell and a method formanufacturing the same.

2. Description of the Related Art

Recently, as existing energy sources such as petroleum and coal areexpected to be depleted, interests in alternative energy sources forreplacing the existing energy sources are increasing. Among thealternative energy sources, solar cells for generating electric energyfrom solar energy have been particularly spotlighted because the solarcells have an abundant energy source that does not cause environmentalpollution.

A solar cell generally includes a substrate and an emitter region, whichare formed of semiconductors of different conductive types, for example,a p-type and an n-type, and electrodes respectively connected to thesubstrate and the emitter region. A p-n junction is formed at aninterface between the substrate and the emitter region.

When light is incident on the solar cell, a plurality of electron-holepairs are produced in the semiconductors. The electron-hole pairs areseparated into electrons and holes. The electrons move to the n-typesemiconductor, for example, the emitter region, and the holes move tothe p-type semiconductor, for example, the substrate. Then, theelectrons and the holes are collected by the different electrodesrespectively connected to the emitter region and the substrate. Theelectrodes are connected to each other using electric wires to therebyobtain electric power.

SUMMARY OF THE INVENTION

In one aspect, there is a solar cell including a substrate containingimpurities of a first conductive type, an emitter region positioned at afront surface of the substrate, the emitter region containing impuritiesof a second conductive type opposite the first conductive type, a backpassivation layer positioned on a back surface of the substrate, theback passivation layer having a plurality of openings, a back surfacefield region containing impurities of the first conductive type, a firstelectrode connected to the emitter region, and a second electrodeconnected to the back surface field region, wherein the back surfacefield region includes a first back surface field region, which ispositioned on the back passivation layer and has a plurality ofopenings, and a second back surface field region, which is positioned atthe back surface of the substrate exposed by the plurality of openingsof the back passivation layer.

The second back surface field region may include a crystalline siliconlayer which is more heavily doped with impurities of the firstconductive type than the substrate. In this instance, an amount of theimpurities of the first conductive type contained in the second backsurface field region may be equal to or more than an amount of theimpurities of the first conductive type contained in the first backsurface field region.

The first back surface field region may include a microcrystallinesilicon layer which is more heavily doped with impurities of the firstconductive type than the substrate.

The first back surface field region may further include an amorphoussilicon layer which is positioned between the back passivation layer andthe microcrystalline silicon layer and contains impurities of the firstconductive type.

A doping concentration of the amorphous silicon layer included in thefirst back surface field region may be lower than a doping concentrationof the microcrystalline silicon layer included in the first back surfacefield region.

The back passivation layer may include an intrinsic amorphous siliconlayer.

The solar cell may further include a dielectric layer which ispositioned on the first back surface field region and has a plurality ofopenings.

The second electrode may physically contact the first back surface fieldregion and the second back surface field region. In this instance, thefirst back surface field region may be spatially separated from thesecond back surface field region, and the first back surface fieldregion and the second back surface field region may be electricallyconnected to each other through the second electrode.

A thickness of the back passivation layer may be about 10 nm to 50 nm. Athickness of the first back surface field region may be about 10 nm to50 nm. A doping depth of the second back surface field region may beabout 3 μm to 5 μm.

A distance between the plurality of openings of the first back surfacefield region may be about 0.15 mm to 1 mm.

The dielectric layer may be formed of silicon nitride (SiNx).

In another aspect, there is a method for manufacturing a solar cellincluding forming an emitter region containing impurities of a secondconductive type opposite a first conductive type at a front surface of asubstrate containing impurities of the first conductive type, forming aback passivation layer including an intrinsic amorphous silicon layer ona back surface of the substrate, forming a first back surface fieldregion on the back passivation layer, selectively irradiating a laserbeam onto the first back surface field region to form a plurality ofopenings in the back passivation layer and the first back surface fieldregion and forming a second back surface field region at the backsurface of the substrate exposed by the plurality of openings of theback passivation layer and the first back surface field region, forminga first electrode connected to the emitter region, and forming a secondelectrode connected to the first back surface field region and thesecond back surface field region.

The forming of the first back surface field region may include forming amicrocrystalline silicon layer, which is more heavily doped withimpurities of the first conductive type than the substrate, on the backpassivation layer.

The forming of the first back surface field region may further includeforming an amorphous silicon layer containing impurities of the firstconductive type, of which a doping concentration is lower than a dopingconcentration of the microcrystalline silicon layer, on the backpassivation layer before forming the microcrystalline silicon layer.

The method may further include forming a dielectric layer on the firstback surface field region, wherein the laser beam is selectivelyirradiated onto the dielectric layer.

A process temperature for forming the dielectric layer may be about 300°C. to 400° C.

The second electrode may be formed using a plating method.

The solar cell and the method for manufacturing the same according toembodiments of the invention includes the back surface field region onthe back passivation layer and in the back surface of the substrateexposed by the plurality of openings of the back passivation layer,thereby further enhancing a back surface field function and furtherimproving efficiency of the solar cell.

Further, because the back surface field region according to theembodiments of the invention includes the microcrystalline siliconlayer, a laser beam having a low energy density may be used to form theback surface field region. Hence, a heat damage of the substrateresulting from the laser beam may be minimized. As a result, thegeneration of a dark saturation current may be minimized, and theefficiency of the solar cell may be further improved.

Further, because the back surface field region according to theembodiments of the invention includes the amorphous silicon layer, apassivation function of the back passivation layer may be furtherenhanced.

Further, because the back passivation layer according to the embodimentsof the invention is thicker than a related art back passivation layer,the passivation function of the back passivation layer may be furtherenhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a partial perspective view of a solar cell according to anexample embodiment of the invention;

FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1;

FIG. 3 is an enlarged view of a portion ‘A’ shown in FIG. 2;

FIG. 4 illustrates a relationship between an energy density of a laserbeam and a dark saturation current generated in a solar cell through theirradiation of the laser beam when the laser beam is irradiated onto aback surface of a substrate to form a back surface field region;

FIG. 5 illustrates an effect obtained when a first back surface fieldregion includes a microcrystalline silicon layer when a laser beam isirradiated onto the microcrystalline silicon layer included in the firstback surface field region to form a second back surface field regionaccording to an embodiment of the invention;

FIG. 6 illustrates an effect of a thickness of a back passivation layeraccording to an embodiment of the invention;

FIGS. 7 to 12 illustrate a method for manufacturing a solar cellaccording to an example embodiment of the invention;

FIG. 13 is a partial perspective view of a solar cell according toanother example embodiment of the invention; and

FIG. 14 is a cross-sectional view taken along line II′-II′ of FIG. 13.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to embodiments of the invention,examples of which are illustrated in the accompanying drawings. Thisinvention may, however, be embodied in many different forms and shouldnot be construed as limited to the embodiments set forth herein.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts. It should be noted thata detailed description of known arts will be omitted if it is determinedthat the known arts can obscure the embodiments of the invention.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. It will be understood that when an elementsuch as a layer, film, region, or substrate is referred to as being “on”another element, it can be directly on the other element or interveningelements may also be present. In contrast, when an element is referredto as being “directly on” another element, there are no interveningelements present. Further, it will be understood that when an elementsuch as a layer, film, region, or substrate is referred to as being“entirely” on other element, it may be on the entire surface of theother element and may not be on a portion of an edge of the otherelement.

Example embodiments of the invention will be described with reference toFIGS. 1 to 14.

FIG. 1 is a partial perspective view of a solar cell according to anexample embodiment of the invention, FIG. 2 is a cross-sectional viewtaken along line II-II of FIG. 1, and FIG. 3 is an enlarged view of aportion ‘A’ shown in FIG. 2.

As shown in FIGS. 1 to 3, a solar cell according to an exampleembodiment of the invention includes a substrate 110, an emitter region120, an anti-reflection layer 130, a back passivation layer 190, adielectric layer 180, a back surface field region 170 including a firstback surface field region 170A and a second back surface field region170B, a first electrode 140, and a second electrode 150.

In the embodiment of the invention, the solar cell including theanti-reflection layer 130 and the dielectric layer 180 is described asan example. However, the anti-reflection layer 130 and the dielectriclayer 180 may be omitted, if necessary or desired. In an aspect ofefficiency of the solar cell, an efficiency of the solar cell includingthe anti-reflection layer 130 and the dielectric layer 180 is greaterthan an efficiency of the solar cell not including the anti-reflectionlayer 130 and the dielectric layer 180. Therefore, the solar cellincluding the anti-reflection layer 130 and the dielectric layer 180 isdescribed as an example of the embodiment of the invention.

The substrate 110 may be a semiconductor substrate formed of siliconcontaining impurities of a first conductive type, for example, p-typeimpurities, though not required. Silicon used in the substrate 110 maybe crystalline silicon such as single crystal silicon andpolycrystalline silicon. If the substrate 110 is of a p-type, thesubstrate 110 may contain impurities of a group III element such asboron (B), gallium (Ga), and indium (In). Alternatively, the substrate110 may be of an n-type and/or may be formed of a semiconductor materialother than silicon. If the substrate 110 is of the n-type, the substrate110 may contain impurities of a group V element such as phosphorus (P),arsenic (As), and antimony (Sb). In the following description, the solarcell is described using the substrate 110 of the n-type as an example.

As shown in FIGS. 1 to 3, the surface of the substrate 110 is texturedto form a textured surface corresponding to an uneven surface having aplurality of uneven portions or having uneven characteristics.

The emitter region 120 is positioned at a front surface of the substrate110, on which light is incident. The emitter region 120 containsimpurities of a second conductive type (for example, a p-type) oppositethe first conductive type (for example, the n-type) of the substrate 110to form a p-n junction along with the substrate 110.

Carriers, i.e., a plurality of electron-hole pairs produced by lightincident on the substrate 110 are separated into electrons and holes dueto the p-n junction between the substrate 110 and the emitter region120. The electrons move to the n-type semiconductor, and the holes moveto the p-type semiconductor. Thus, when the substrate 110 is of then-type and the emitter region 120 is of the p-type, the separatedelectrons move to the substrate 110 and the separated holes move to theemitter region 120. Hence, the electrons become major carriers in thesubstrate 110, and the holes become major carriers in the emitter region120.

Because the emitter region 120 forms the p-n junction along with thesubstrate 110, the emitter region 120 may be of the n-type when thesubstrate 110 is of the p-type unlike the embodiment described above. Inthis instance, the separated electrons move to the emitter region 120,and the separated holes move to the substrate 110.

Returning to the embodiment of the invention, when the emitter region120 is of the p-type, the emitter region 120 may be formed by doping thesubstrate 110 with impurities of a group III element such as B, Ga, andIn. On the contrary, if the emitter region 120 is of the n-type, theemitter region 120 may be formed by doping the substrate 110 withimpurities of a group V element such as P, As, and Sb.

The emitter region 120 formed at the front surface of the substrate 110may include a first region, which overlaps and contacts the firstelectrode 140, and a second region, which does not overlap or contactthe first electrode 140. The first region and the second region of theemitter region 120 may have different impurity doping concentrations.

In this instance, the first region of the emitter region 120, whichoverlaps and contacts the first electrode 140, is formed as a heavilydoped region having a relatively high impurity doping concentration.Further, the second region of the emitter region 120, which does notoverlap or contact the first electrode 140, is formed as a lightly dopedregion having an impurity doping concentration lower than the heavilydoped region.

The anti-reflection layer 130 is positioned on the emitter region 120.The anti-reflection layer 130 may have a single-layered structureincluding any one of an aluminum oxide (Al₂O₃) layer, a silicon nitride(SiNx) layer, a silicon oxide (SiOx) layer, and a silicon oxynitride(SiOxNy) layer, or a multi-layered structure including at least two ofthe layers.

FIGS. 1 and 2 show the anti-reflection layer 130 having a double-layeredstructure as an example. In this instance, the anti-reflection layer 130includes a first anti-reflection layer 130 b formed on the emitterregion 120 and a second anti-reflection layer 130 a formed on the firstanti-reflection layer 130 b.

In the embodiment of the invention, the first anti-reflection layer 130b is formed of aluminum oxide (Al₂O₃) and has a passivation function aswell as an anti-reflection function.

Further, it is preferable, but not required, that the secondanti-reflection layer 130 a is formed of silicon nitride (SiNx). Othermaterials may be used. For example, the second anti-reflection layer 130a may be formed of silicon oxide (SiOx) or silicon oxynitride (SiOxNy).

The anti-reflection layer 130 reduces a reflectance of light incident onthe solar cell and selectively increases light of a predeterminedwavelength band, thereby increasing the efficiency of the solar cell.

The first electrode 140 physically contacts the emitter region 120 andis electrically connected to the emitter region 120. As shown in FIG. 1,the first electrode 140 includes a plurality of finger electrodes 141and a plurality of front bus bars 143.

The finger electrodes 141 are positioned on the emitter region 120 andare electrically connected to the emitter region 120. The fingerelectrodes 141 are separated from one another by a uniform distance andextend in a fixed direction. The finger electrodes 141 collect carriers(for example, holes) moving to the emitter region 120.

The front bus bars 143 are positioned on the same level layer as thefinger electrodes 141 on the emitter region 120. The front bus bars 143electrically connect the finger electrodes 141 to one another and extendin a direction crossing the finger electrodes 141. The front bus bars143 are connected to an interconnector for connecting solar cells. Thefront bus bars 143 collect carriers, which are collected by the fingerelectrodes 141 and move, and output the carriers to an external device.

The finger electrodes 141 and the front bus bars 143 of the firstelectrode 140 may be formed of the same conductive material, forexample, at least one selected from the group consisting of nickel (Ni),copper (Cu), silver (Ag), aluminum (Al), tin (Sn), zinc (Zn), indium(In), titanium (Ti), gold (Au), and a combination thereof. Otherconductive materials may be used.

As shown in FIGS. 1 and 2, the back passivation layer 190 is positionedon a back surface opposite the front surface of the substrate 110, onwhich light is incident. The back passivation layer 190 includes anintrinsic (called i-type) amorphous silicon layer formed using a plasmaenhanced chemical vapor deposition (PECVD) method, for example. The backpassivation layer 190 is entirely formed on the back surface of thesubstrate 110 and has a plurality of openings.

The back passivation layer 190 prevents or reduces a recombinationand/or a disappearance of carriers at and around the back surface of thesubstrate 110 and improves an inner reflectance of light passing throughthe substrate 110, thereby increasing reincidence of light passingthrough the substrate 110.

The back surface field region 170 contains impurities of the firstconductive type. As shown in FIGS. 1 to 3, the back surface field region170 includes the first back surface field region 170A and the secondback surface field region 170B.

The first back surface field region 170A is positioned on the backpassivation layer 190 and has a plurality of openings. The second backsurface field region 170B is formed at the back surface of the substrate110 exposed by the plurality of openings included in the backpassivation layer 190.

The plurality of openings included in the first back surface fieldregion 170A overlap the plurality of openings of the back passivationlayer 190. Namely, the openings of the first back surface field region170A are formed at the same location as the openings of the backpassivation layer 190, and a width or a diameter of the opening of thefirst back surface field region 170A may be the same as the opening ofthe back passivation layer 190.

The first back surface field region 170A may have a single-layeredstructure or a multi-layered structure. Preferably, but not required,the first back surface field region 170A may have the multi-layeredstructure. If the first back surface field region 170A has themulti-layered structure, one layer of the first back surface fieldregion 170A may be formed of amorphous silicon material, and anotherlayer may be formed of microcrystalline silicon material.

The first back surface field region 170A is formed on the backpassivation layer 190 using the PECVD method.

The second back surface field region 170B is positioned at the substrate110. If the substrate 110 contains crystalline silicon material, thesecond back surface field region 170B may include a crystalline siliconlayer which is more heavily doped with impurities of the firstconductive type than the substrate 110.

The second back surface field region 170B is formed by irradiating alaser beam onto the first back surface field region 170A and diffusingimpurities of the first conductive type contained in the first backsurface field region 170A into the substrate 110.

The back surface field region 170 performs a back surface field functionand forms a potential barrier generating a potential difference betweenthe substrate 110 and the back surface field region 170 by a differencebetween impurity concentrations of the substrate 110 and the backsurface field region 170.

In this instance, when the substrate 110 is of the n-type and theemitter region 120 is of the p-type, the back surface field region 170forms an n-type electric field higher than the substrate 110. Hence, theback surface field region 170 makes it easier for the major carriers(i.e., electrons) of the substrate 110 to move to the second electrode150 through the back surface field region 170 and prevents the majorcarriers (i.e., holes) of the emitter region 120 from moving to thesecond electrode 150.

Because the first back surface field region 170A is formed of theamorphous silicon material or the microcrystalline silicon material, thefirst back surface field region 170A may perform the passivationfunction in the same manner as the back passivation layer 190.

The dielectric layer 180 is positioned on the back surface field region170 and has a plurality of openings at a location overlapping theopenings of the back surface field region 170. Namely, the opening ofthe dielectric layer 180 is formed at the same location as the openingof the back surface field region 170, and a width or a diameter of theopening of dielectric layer 180 may be the same as the opening of theback surface field region 170.

The dielectric layer 180 may be formed of at least one of siliconnitride (SiNx), silicon oxide (SiOx), and silicon oxynitride (SiOxNy)and may have a single-layered structure or a multi-layered structure.

Preferably, but not required, the dielectric layer 180 may be formed ofsilicon nitride (SiNx) having a relatively low process temperature, soas to minimize a heat damage of the back passivation layer 190 and thefirst back surface field region 170A considering that the backpassivation layer 190 and the first back surface field region 170Acontain the amorphous silicon material.

The dielectric layer 180 functions to partially bring the secondelectrode 150 into contact with the substrate 110 and the back surfacefield region 170 only through the plurality of openings of thedielectric layer 180. Namely, the dielectric layer 180 prevents thesecond electrode 150 from contacting the entire back surface of thesubstrate 110 and the entire back surface of the first back surfacefield region 170A.

The second electrode 150 contains a conductive material and ispositioned on a back surface of the dielectric layer 180. The secondelectrode 150 includes a plurality of connection electrodes 155, whichare respectively positioned in the plurality of openings included ineach of the back passivation layer 190, the first back surface fieldregion 170A, and the dielectric layer 180.

Hence, the second electrode 150 is electrically connected to the firstback surface field region 170A and the second back surface field region170B. Namely, as shown in FIGS. 1 to 3, the second electrode 150directly contacts the first back surface field region 170A and thesecond back surface field region 170B and is electrically connected tothem.

The second electrode 150 includes the plurality of connection electrodes155, a back electrode layer 151, and a plurality of back bus bars 153.

The plurality of connection electrodes 155 are respectively positionedin the plurality of openings included in each of the back passivationlayer 190, the first back surface field region 170A, and the dielectriclayer 180. The plurality of connection electrodes 155 directly contactthe second back surface field region 170B positioned at the substrate110.

It is preferable, but not required, that the plurality of connectionelectrodes 155 are formed through a plating method, which is performedat a relatively low process temperature, so as to minimize a damage ofthe back passivation layer 190 and the first back surface field region170A resulting from heat considering that the back passivation layer 190and the first back surface field region 170A contain the amorphoussilicon material. As described above, because the connection electrodes155 may be formed through the plating method at the low processtemperature, the passivation function of the back passivation layer 190may be maximized.

The back electrode layer 151 is entirely positioned on the dielectriclayer 180 except a formation area of the back bus bars 153. The backelectrode layer 151 may directly contact the plurality of connectionelectrodes 155.

The back electrode layer 151 may be formed of at least one selected fromthe group consisting of nickel (Ni), copper (Cu), silver (Ag), tin (Sn),zinc (Zn), indium (In), titanium (Ti), gold (Au), and a combinationthereof. Other conductive materials may be used.

The back electrode layer 151 is formed through one of a plating methodand an evaporation method, which are performed at a relatively lowprocess temperature, so as to minimize a heat damage of the backpassivation layer 190 and the first back surface field region 170A.Other methods, which are performed at a relatively low processtemperature, may be used.

The plurality of back bus bars 153 are positioned on the back surfacefield region 170 and directly contact and are electrically connected tothe back electrode layer 151. The back bus bars 153 extend in the samedirection as the front bus bars 143 to form a stripe arrangement. Theback bus bars 153 may be positioned opposite the front bus bars 143.

The back bus bars 153 directly contact the interconnector in the samemanner as the front bus bars 143 and output carriers, which arecollected from the substrate 110 to the back electrode layer 151, to theexternal device.

It is preferable, but not required, that the back bus bars 153 areformed of a conductive material, for example, silver (Ag). However, theback bus bars 153 may be formed of at least one selected from the groupconsisting of nickel (Ni), copper (Cu), aluminum (Al), tin (Sn), zinc(Zn), indium (In), titanium (Ti), gold (Au), and a combination thereof.Other conductive materials may be used.

The back bus bars 153 are formed through one of a plating method and anevaporation method, which are performed at a relatively low processtemperature, in the same manner as the back electrode layer 151.

So far, the embodiment of the invention described the structure of thesecond electrode 150 including the back electrode layer 151 and theplurality of back bus bars 153. However, other structures may be usedfor the second electrode 150. This is described with reference to FIGS.13 and 14.

FIG. 13 is a partial perspective view of a solar cell according toanother example embodiment of the invention, and FIG. 14 is across-sectional view taken along line II′-II′ of FIG. 13.

Since configuration of the solar cell illustrated in FIGS. 13 and 14 issubstantially the same as configuration of the solar cell illustrated inFIGS. 1 to 3 except a structure of a second electrode 150′, a furtherdescription may be briefly made or may be entirely omitted.

The second electrode 150′ has the same structure as a first electrode140 so as to form a structure of a bifacial solar cell. Namely, thesecond electrode 150′ includes a plurality of back finger electrodes151′ extending in a first direction and a plurality of back bus bars153′ which extend in a second direction crossing the first direction andconnect the plurality of back finger electrodes 151′ to one another.

A back passivation layer 190, a first back surface field region 170A,and a dielectric layer 180 each have a plurality of openings which areformed at an overlap location of the components 190, 170A, and 180 andexpose a second back surface field region 170B formed at a back surfaceof a substrate 110. Because the openings are filled with the back fingerelectrodes 151′, the second electrode 150′ is electrically connected tothe substrate 110 through the second back surface field region 170B.

An operation of the solar cell having the above-described structureaccording to the embodiments of the invention is described below.

When light irradiated to the solar cell is incident on the substrate 110through the anti-reflection layer 130 and the emitter region 120, aplurality of electron-hole pairs are generated in the substrate 110 bylight energy produced based on the incident light. In this instance, areflection loss of the light incident on the substrate 110 is reduced bythe anti-reflection layer 130, and thus an amount of light incident onthe substrate 110 increases.

The electron-hole pairs are separated into electrons and holes due tothe p-n junction of the substrate 110 and the emitter region 120. Theelectrons move to the n-type substrate 110, and the holes move to thep-type emitter region 120. The holes moving to the emitter region 120are collected by the finger electrodes 141 and then are transferred andcollected to the front bus bars 143. The electrons moving to thesubstrate 110 are collected to the back electrode layer 151 through theconnection electrodes 155 and then are transferred to the back bus bars153. When the front bus bars 143 are connected to the back bus bars 153using conductive wires, current flows therein to thereby enable use ofthe current for electric power.

As described above, in the solar cell according to the embodiment of theinvention, the back surface field region 170 includes the first backsurface field region 170A, which is positioned on the back surface ofthe back passivation layer 190 and has the plurality of openings, andthe second back surface field region 170B which is positioned in theback surface of the substrate 110 exposed by the plurality of openingsof the back passivation layer 190.

In the embodiment of the invention, the first back surface field region170A performs both the back surface field function and the passivationfunction, and the second back surface field region 170B performs theback surface field function.

The structure of the solar cell according to the embodiment of theinvention prevents or reduces carriers moving to the second electrode150 from being recombined and/or disappearing at and around the backsurface of the substrate 110, thereby increasing an open-circuit circuitJsc and a fill factor F.F of the solar cell. As a result, the efficiencyof the solar cell may increase.

More specifically, the structure of the solar cell according to theembodiment of the invention forms the second back surface field region170B at the back surface of the substrate 110, forms the backpassivation layer 190 on the back surface of the substrate 110, andforms the first back surface field region 170A, which performs both theback surface field function and the passivation function, on the backpassivation layer 190. Thus, in the embodiment of the invention, becauseboth the back passivation layer 190 and the first back surface fieldregion 170A perform the passivation function of the back surface of thesubstrate 110, the passivation function is further enhanced. Further,because both the first back surface field region 170A and the secondback surface field region 170B perform the back surface field functionof the back surface of the substrate 110, the back surface fieldfunction is further enhanced.

When the major carriers (for example, electrons) of the substrate 110move to the back surface of the substrate 110, the embodiment of theinvention reduces an amount of carriers recombined by dangling bondsexisting at and around the back surface of the substrate 110 and thusreduces a magnitude of a dark saturation current Jo generating thecombination of the carriers. Further, the embodiment of the inventionmakes it easier for the major carriers (for example, electrons) of thesubstrate 110 to move to the second electrode 150 through the backsurface field region 170, and at the same time prevents the majorcarriers (for example, holes) of the emitter region 120 from moving tothe second electrode 150.

In the embodiment of the invention, the second back surface field region170B includes the crystalline silicon layer which is more heavily dopedwith impurities of the first conductive type than the substrate 110.Hence, the solar cell according to the embodiment of the invention mayfurther reduce a resistance of the second back surface field region170B, and thus the movement of carriers from the substrate 110 to thesecond electrode 150 may be more smoothly performed.

Further, as shown in FIG. 3, the first back surface field region 170Apositioned on the back passivation layer 190 includes a microcrystallinesilicon layer 170A2 which is more heavily doped with impurities of thefirst conductive type than the substrate 110.

The microcrystalline silicon layer 170A2 of the first back surface fieldregion 170A makes it possible to use a laser beam having a lower laserenergy density when a laser beam is irradiated onto the back surface ofthe substrate 110 to form the second back surface field region 170B in aprocess for manufacturing the solar cell.

Hence, the microcrystalline silicon layer 170A2 of the first backsurface field region 170A prevents or reduces the damage of thesubstrate 110 resulting from the laser beam used when the second backsurface field region 170B is formed at the back surface of the substrate110, thereby minimizing the generation of the dark saturation currentJo. Further, the microcrystalline silicon layer 170A2 of the first backsurface field region 170A causes the second back surface field region170B formed at the back surface of the substrate 110 to have a sheetresistance of a desired magnitude. This is described in detail belowwith reference to FIGS. 4 and 5.

The first back surface field region 170A further includes an amorphoussilicon layer 170A1 which is positioned between the back passivationlayer 190 and the microcrystalline silicon layer 170A2 and containsimpurities of the first conductive type. In the first back surface fieldregion 170A, a doping concentration of the amorphous silicon layer 170A1is lower than a doping concentration of the microcrystalline siliconlayer 170A2.

The amorphous silicon layer 170A1 of the first back surface field region170A makes it possible to form an ohmic contact between the backpassivation layer 190 including the intrinsic amorphous silicon layerand the microcrystalline silicon layer 170A2 of the first back surfacefield region 170A.

The amorphous silicon layer 170A1 of the first back surface field region170A may further enhance the passivation function of the backpassivation layer 190 including the intrinsic amorphous silicon layer.

A sheet resistance of the first back surface field region 170A graduallydecreases as it goes from the amorphous silicon layer 170A1 of arelatively low concentration to the microcrystalline silicon layer 170A2of a relatively high concentration. Hence, the movement of carriers fromthe first back surface field region 170A to the second electrode 150 maybe more smoothly performed.

Each connection electrode 155 of the second electrode 150 directlycontacts the first back surface field region 170A and the second backsurface field region 170B. In this instance, the first back surfacefield region 170A and the second back surface field region 170B arespatially separated from each other, but are electrically connected toeach other through the second electrode 150.

A thickness T170A of the first back surface field region 170A is about10 nm to 50 nm, and a doping depth D170B of the second back surfacefield region 170B is about 3 μm to 5 μm.

A distance D1 between the plurality of openings of the first backsurface field region 170A is about 0.15 mm to 1 mm.

A plane shape of the plurality of openings of the first back surfacefield region 170A may be a line shape or a dot shape.

More specifically, when the plane shape of the plurality of openings ofthe first back surface field region 170A is the line shape, a distancebetween the lines is about 0.3 mm to 1 mm. Further, when the plane shapeof the plurality of openings of the first back surface field region 170Ais the dot shape, a distance between the dots is 0.15 mm to 1 mm.

In the embodiment of the invention, the laser beam is irradiated ontothe substrate 110 to form the plurality of openings of the first backsurface field region 170A. In this instance, when the distance D1between the openings is excessively narrow, an area of the substrate110, onto which the laser beam is irradiated, excessively increases.Hence, the characteristics of the substrate 110 may be reduced. On thecontrary, when the distance D1 between the openings is excessively wide,the fill factor of the solar cell may be reduced. Therefore, thedistance D1 between the openings of the first back surface field region170A is defined as described above.

As described above, the dielectric layer 180 may be formed of at leastone of silicon nitride (SiNx), silicon oxide (SiOx), and siliconoxynitride (SiOxNy). Preferably, but not required, the dielectric layer180 is formed of silicon nitride (SiNx). In the embodiment of theinvention, because the dielectric layer 180 is formed of silicon nitride(SiNx) which is processed at a relatively low process temperature (forexample, about 300° C. to 400° C.), it is possible to minimize a heatdamage of the back passivation layer 190 including the intrinsicamorphous silicon layer or the amorphous silicon layer 170A1 of thefirst back surface field region 170A resulting from the processtemperature of the dielectric layer 180 in the process for forming thedielectric layer 180.

When the first back surface field region 170A and the second backsurface field region 170B in the solar cell having the structureillustrated in FIGS. 1 to 3 are formed, an effect obtained when thefirst back surface field region 170A includes the microcrystallinesilicon layer 170A2 is described below with reference to FIGS. 4 and 5.

FIG. 4 illustrates a relationship between an energy density of the laserbeam and a dark saturation current Jo generated in the solar cellthrough the irradiation of the laser beam when the laser beam isirradiated onto the back surface of the substrate 110 to form the backsurface field region 170.

As shown in FIG. 4, the dark saturation current Jo and the energydensity of the laser beam are proportional to each other.

As described above, the dark saturation current Jo is a current valuegenerating the combination of carriers. Thus, as the dark saturationcurrent Jo increases, an amount of combined carriers increases. Hence, ashort circuit current Jsc and the efficiency of the solar cell arereduced.

In other words, a passivation effect of the solar cell increases as thedark saturation current Jo decreases, and also the passivation effect ofthe solar cell decreases as the dark saturation current Jo increases.Thus, the less the dark saturation current Jo is, the greater theefficiency of the solar cell is.

As shown in FIG. 4, impurities of the first conductive type are diffusedinto the back surface of the substrate 110, and the laser beam isselectively irradiated onto the back surface of the substrate 110 tolocally form the second back surface field region 170B at the backsurface of the substrate 110.

In this instance, the energy density of the laser beam has to increaseso as to properly reduce a sheet resistance of the second back surfacefield region 170B selectively formed at the back surface of thesubstrate 110.

However, as shown in FIG. 4, when the laser energy density increases,the dark saturation current Jo increases. Hence, even when the secondback surface field region 170B is formed at the back surface of thesubstrate 110, the efficiency of the solar cell does not increase to adesired level.

However, as in the embodiment of the invention, when the first backsurface field region 170A includes the microcrystalline silicon layer170A2, the sheet resistance of the second back surface field region 170Bmay be properly reduced to a desired level even if a laser beam having arelatively low energy density is used.

Namely, in the embodiment of the invention, the microcrystalline siliconlayer 170A2 included in the first back surface field region 170A may beused as a dopant layer for forming the second back surface field region170B. The laser beam may be selectively irradiated onto themicrocrystalline silicon layer 170A2 used as the dopant layer to locallyform the second back surface field region 170B, is more heavily dopedthan the substrate 110, at the back surface of the substrate 110.

FIG. 5 illustrates an effect obtained when the first back surface fieldregion 170A includes the microcrystalline silicon layer 170A2 when thelaser beam is irradiated onto the microcrystalline silicon layer 170A2included in the first back surface field region 170A to form the secondback surface field region 170B according to the embodiment of theinvention.

In FIG. 5, x-axis indicates a laser energy density, and y-axis indicatesthe sheet resistance of the second back surface field region 170B formedat the back surface of the substrate 110.

In FIG. 5, (a) is a comparative example where when the laser beam isirradiated onto the first back surface field region 170A used as adopant to form the second back surface field region 170B at the backsurface of the substrate 110, the first back surface field region 170Adoes not include the microcrystalline silicon layer 170A2 and includesan amorphous silicon layer as the dopant layer. Further, (b) of FIG. 5is the embodiment of the invention where when the laser beam isirradiated onto the first back surface field region 170A used as adopant to form the second back surface field region 170B at the backsurface of the substrate 110, the first back surface field region 170Aincludes the microcrystalline silicon layer 170A2. (b) of FIG. 5according to the embodiment of the invention may be applied to anexample where the first back surface field region 170A includes theamorphous silicon layer 170A1 as well as the microcrystalline siliconlayer 170A2 as shown in FIG. 3.

As shown in (a) and (b) of FIG. 5, in the comparative example and theembodiment of the invention, the energy density of the laser beam has toincrease so as to form the second back surface field region 170B havinga sufficiently low sheet resistance at the back surface of the substrate110.

As shown in (a) and (b) of FIG. 5, when the energy density of the laserbeam is equal to or less than about 17 J/cm², the sheet resistance ofthe second back surface field region 170B sharply decreases. However,when the energy density of the laser beam is greater than about 17J/cm², the sheet resistance of the second back surface field region 170Bgradually decreases. Further, the sheet resistance of the second backsurface field region 170B in the embodiment of the invention is lessthan the sheet resistance of the second back surface field region 170Bin the comparative example depending on the energy density of the laserbeam.

For example, when the energy density of the laser beam is equal to orless than about 100 J/cm² (i.e., when the energy density of the laserbeam is about 20 J/cm², 40 J/cm², 60 J/cm², and 80 J/cm²), the sheetresistance of the second back surface field region 170B in theembodiment of the invention shown in (b) of FIG. 5 is much less than thesheet resistance of the second back surface field region 170B in thecomparative example shown in (a) of FIG. 5.

More specifically, when the back surface field region 170 is formed atthe back surface of the substrate 110 using the laser beam having theenergy density of about 20 J/cm², the sheet resistance of the secondback surface field region 170B in the comparative example shown in (a)of FIG. 5 is about 33Ω. On the other hand, the sheet resistance of thesecond back surface field region 170B in the embodiment of the inventionshown in (b) of FIG. 5 is about 14Ω and is much less than thecomparative example.

When the sheet resistance of the second back surface field region 170Brequired in the solar cell is equal to or less than about 20Ω, the laserbeam having the energy density equal to or greater than about 83 J/cm²has to be used in the comparative example shown in (a) of FIG. 5.

On the other hand, in the embodiment of the invention shown in (b) ofFIG. 5, the laser beam having the energy density of about 16 J/cm² whichis much less than about 83 J/cm² may be used. Hence, the dark saturationcurrent Jo may be greatly reduced as shown in FIG. 4, and an amount ofcombined carriers may greatly decrease.

As a result, the short circuit current Jsc and the efficiency of thesolar cell may further increase.

Further, in the solar cell according to the embodiment of the invention,a thickness T190 of the back passivation layer 190 including theintrinsic amorphous silicon layer may be about 10 nm to 50 nm, so as tofurther reduce the dark saturation current Jo.

As described above, when the thickness T190 of the back passivationlayer 190 is equal to or greater than about 10 nm, the generation of thedark saturation current Jo is further reduced, and the passivationeffect of the back passivation layer 190 further increases. Further, thethickness T190 of the back passivation layer 190 is set to be equal toor less than about 50 nm in consideration of the manufacturing time andthe manufacturing cost of the solar cell in a state where the darksaturation current Jo is sufficiently reduced.

FIG. 6 illustrates an effect of the thickness of the back passivationlayer 190 according to the embodiment of the invention.

In FIG. 6, (a) is a comparative example where the dark saturationcurrent Jo generated in the solar cell is measured when the thicknessT190 of the back passivation layer 190 is about 2.5 nm, and (b) is theembodiment of the invention where the dark saturation current Jogenerated in the solar cell is measured when the thickness T190 of theback passivation layer 190 is about 20 nm.

As shown in FIG. 6, when the thickness T190 of the back passivationlayer 190 is relatively thin as in the comparative example shown in (a)of FIG. 6, the dark saturation current Jo has a relatively high value ofabout 81 fA/cm². On the other hand, when the thickness T190 of the backpassivation layer 190 is relatively thick (for example, about 10 nm to50 nm) as in the embodiment of the invention shown in (b) of FIG. 6, thedark saturation current Jo is relatively reduced.

Accordingly, when the thickness T190 of the back passivation layer 190is about 10 nm to 50 nm as in the embodiment of the invention, the darksaturation current Jo of the solar cell may be further reduced. As aresult, the short circuit current Jsc and the efficiency of the solarcell may further increase.

As described above, the solar cell according to the embodiment of theinvention is configured so that the back surface field region 170includes the first back surface field region 170A positioned on the backsurface of the back passivation layer 190 and the second back surfacefield region 170B positioned in the back surface of the substrate 110exposed through the plurality of openings of the back passivation layer190. Hence, the passivation function and the back surface field functionof the solar cell may be further enhanced.

Further, the solar cell according to the embodiment of the invention isconfigured so that the first back surface field region 170A includes themicrocrystalline silicon layer 170A2 which is more heavily doped withimpurities of the first conductive type than the substrate 110. Hence,the dark saturation current Jo of the solar cell may be further reduced,and the passivation function of the solar cell may be further enhanced.

Further, the solar cell according to the embodiment of the invention isconfigured so that the back passivation layer 190 includes the intrinsicamorphous silicon layer and the thickness T190 of the back passivationlayer 190 is about 10 nm to 50 nm. Hence, the passivation function ofthe solar cell may be further enhanced.

So far, the structure of the solar cell according to the embodiment ofthe invention was described. Hereinafter, a method for manufacturing thesolar cell according to the embodiment of the invention is described.

FIGS. 7 to 12 illustrate a method for manufacturing the solar cellaccording to the embodiment of the invention.

As shown in FIG. 7, an emitter region 120 containing impurities of asecond conductive type opposite a first conductive type is formed at afront surface of a substrate 110 containing impurities of the firstconductive type.

As shown in FIG. 7, both a front surface and a back surface of thesubstrate 110 may be textured to form a textured surface correspondingto an uneven surface having a plurality of uneven portions or havinguneven characteristics. Alternatively, only the front surface of thesubstrate 110 may be textured to form a textured surface correspondingto an uneven surface having a plurality of uneven portions or havinguneven characteristics.

The substrate 110 is placed in a thermal diffusion furnace in a statethe substrate 110 contains the impurities of the first conductive typeand the surface of the substrate 110 is textured to form the texturedsurface. Then, a process gas containing impurities of the secondconductive type is diffused into the front surface of the substrate 110to form the emitter region 120.

Alternatively, a dopant paste containing impurities of the secondconductive type may be applied to the front surface of the substrate 110and may be diffused into the thermal diffusion furnace to form theemitter region 120. As described above, a method for forming the emitterregion 120 is not particularly limited.

Next, as shown in FIG. 8, a back passivation layer 190 including anintrinsic amorphous silicon layer is formed on the back surface of thesubstrate 110, and then a first back surface field region 170A is formedon the back passivation layer 190. The first back surface field region170A includes an amorphous silicon layer 170A1 and a microcrystallinesilicon layer 170A2.

A process for forming the first back surface field region 170A includesforming the amorphous silicon layer 170A1 containing impurities of thefirst conductive type on the back passivation layer 190 and forming themicrocrystalline silicon layer 170A2, which is more heavily doped withimpurities of the first conductive type than the substrate 110, on theamorphous silicon layer 170A1.

In the embodiment of the invention, a doping concentration of theamorphous silicon layer 170A1 may be lower than a doping concentrationof the microcrystalline silicon layer 170A2.

FIG. 8 shows an example where the first back surface field region 170Aincludes the amorphous silicon layer 170A1 and the microcrystallinesilicon layer 170A2. However, the amorphous silicon layer 170A1 may beomitted, if necessary or desired.

If the amorphous silicon layer 170A1 is omitted, the microcrystallinesilicon layer 170A2 of the first back surface field region 170A maydirectly contact the surface of the back passivation layer 190.

As shown in FIG. 8, after the first back surface field region 170A isformed, a dielectric layer 180 formed of silicon nitride (SiNx) isformed on the first back surface field region 170A. The dielectric layer180 is formed at a process temperature of about 300° C. to 400° C.

Because the dielectric layer 180 is formed at the relatively low processtemperature, a reduction or degradation in characteristics of the backpassivation layer 190 formed of intrinsic amorphous silicon may beminimized. Hence, a reduction in a passivation function of the backpassivation layer 190 may be minimized.

Alternatively, other materials may be used for the dielectric layer 180.For example, the dielectric layer 180 may be formed of silicon oxide(SiOx) and silicon oxynitride (SiOxNy) which are processed at a processtemperature higher than silicon nitride (SiNx), instead of siliconnitride (SiNx).

Next, as shown in FIG. 9, a laser beam LB is selectively irradiated ontoa portion RA of the dielectric layer 180, so that the back passivationlayer 190, the first back surface field region 170A, and the dielectriclayer 180 formed at the back surface of the substrate 110 each have aplurality of openings OP as shown in FIG. 10.

As shown in FIG. 9, when the laser beam LB is selectively irradiatedonto the portion RA of the dielectric layer 180, the impurities of thefirst conductive type contained in the first back surface field region170A are diffused into the back surface of the substrate 110 through thelaser beam LB.

The portion RA of the dielectric layer 180, onto which the laser beam LBis irradiated, is etched and removed by the laser beam LB. A siliconmaterial forming the first back surface field region 170A and the backpassivation layer 190 is melted in an area of the first back surfacefield region 170A and an area of the back passivation layer 190, ontowhich the laser beam LB is irradiated. Then, the silicon material isabsorbed in the back surface of the substrate 110 and is recrystallized.

Further, an oxide layer may be formed on the back surface of thesubstrate 110 exposed by the openings OP of each of the dielectric layer180, the first back surface field region 170A, and the back passivationlayer 190 through the irradiation of the laser beam LB. The oxide layeris removed through a cleaning process after the irradiation of the laserbeam LB is completed.

A plane shape of the laser beam LB, which is selectively irradiated ontothe portion RA of the dielectric layer 180 using a laser irradiationdevice LRA, may be a line shape or a dot shape. In this instance, adistance between the portions RA may be 0.15 mm to 1 mm. As shown inFIG. 10, the back passivation layer 190, the first back surface fieldregion 170A, and the dielectric layer 180 each have the plurality ofopenings OP through the irradiation of the laser beam LB. Impurities ofthe first conductive type contained in the first back surface fieldregion 170A are diffused into the back surface of the substrate 110 dueto the laser beam LB. The silicon material forming the first backsurface field region 170A and the back passivation layer 190 is meltedin an area of the first back surface field region 170A and an area ofthe back passivation layer 190, onto which the laser beam LB isirradiated. Then, the silicon material is absorbed in the back surfaceof the substrate 110 and is recrystallized. Hence, a second back surfacefield region 170B is formed in the back surface of the substrate 110exposed by the plurality of openings OP.

Next, as shown in FIG. 11, a plurality of connection electrodes 155 of asecond electrode 150, which is connected to the first back surface fieldregion 170A and the second back surface field region 170B, are formed.It is preferable, but not required, that the connection electrodes 155of the second electrode 150 are formed using a plating method so as tominimize a heat damage of the back passivation layer 190 and theamorphous silicon layer 170A1 included in the first back surface fieldregion 170A.

Next, as shown in FIG. 12, an anti-reflection layer 130 and a firstelectrode 140 are sequentially formed on the emitter region 120 formedat the front surface of the substrate 110. A back electrode layer 151and a plurality of back bus bars 153 are formed on the dielectric layer180 positioned on the back surface of the substrate 110 to complete thesecond electrode 150 including the back electrode layer 151, the backbus bars 153, and the connection electrodes 155.

The embodiment of the invention describes that the anti-reflection layer130 or the first electrode 140 is formed on the front surface of thesubstrate 110 after the back passivation layer 190, the first backsurface field region 170A, the second back surface field region 170B,and the dielectric layer 180 are formed on the back surface of thesubstrate 110. However, unlike this, after the emitter region 120 isformed at the front surface of the substrate 110, the anti-reflectionlayer 130 or the first electrode 140 may be formed irrespective of theformation order.

For example, after the emitter region 120 is formed at the front surfaceof the substrate 110, the anti-reflection layer 130 or the firstelectrode 140 may be formed before the back passivation layer 190, thefirst back surface field region 170A, the second back surface fieldregion 170B, and the dielectric layer 180 are formed.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the scope of the principles of thisdisclosure. More particularly, various variations and modifications arepossible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A solar cell comprising: a substrate containingimpurities of a first conductive type; an emitter region positioned at afront surface of the substrate, the emitter region containing impuritiesof a second conductive type opposite the first conductive type; a backpassivation layer positioned on a back surface of the substrate, theback passivation layer having a plurality of openings; a back surfacefield region containing impurities of the first conductive type; a firstelectrode connected to the emitter region; and a second electrodeconnected to the back surface field region, wherein the back surfacefield region includes a first back surface field region, which ispositioned on the back passivation layer and has a plurality ofopenings, and a second back surface field region, which is positioned atthe back surface of the substrate exposed by the plurality of openingsof the back passivation layer.
 2. The solar cell of claim 1, wherein thesecond back surface field region includes a crystalline silicon layerwhich is more heavily doped with impurities of the first conductive typethan the substrate.
 3. The solar cell of claim 1, wherein the first backsurface field region includes a microcrystalline silicon layer which ismore heavily doped with impurities of the first conductive type than thesubstrate.
 4. The solar cell of claim 3, wherein the first back surfacefield region further includes an amorphous silicon layer which ispositioned between the back passivation layer and the microcrystallinesilicon layer and contains impurities of the first conductive type. 5.The solar cell of claim 4, wherein a doping concentration of theamorphous silicon layer included in the first back surface field regionis lower than a doping concentration of the microcrystalline siliconlayer included in the first back surface field region.
 6. The solar cellof claim 1, wherein the back passivation layer includes an intrinsicamorphous silicon layer.
 7. The solar cell of claim 1, furthercomprising a dielectric layer which is positioned on the first backsurface field region and has a plurality of openings.
 8. The solar cellof claim 1, wherein the second electrode physically contacts the firstback surface field region and the second back surface field region. 9.The solar cell of claim 1, wherein the first back surface field regionis physically separated from the second back surface field region. 10.The solar cell of claim 1, wherein the first back surface field regionand the second back surface field region are electrically connected toeach other through the second electrode.
 11. The solar cell of claim 1,wherein a thickness of the back passivation layer is 10 nm to 50 nm. 12.The solar cell of claim 1, wherein a thickness of the first back surfacefield region is 10 nm to 50 nm.
 13. The solar cell of claim 1, wherein adoping depth of the second back surface field region is 3 μm to 5 μm.14. The solar cell of claim 1, wherein a distance between the pluralityof openings of the first back surface field region is 0.15 mm to 1 mm.15. The solar cell of claim 7, wherein the dielectric layer is formed ofsilicon nitride (SiNx).
 16. A method for manufacturing a solar cellcomprising: forming an emitter region containing impurities of a secondconductive type opposite a first conductive type at a front surface of asubstrate containing impurities of the first conductive type; forming aback passivation layer including an intrinsic amorphous silicon layer ona back surface of the substrate; forming a first back surface fieldregion on the back passivation layer; selectively irradiating a laserbeam onto the first back surface field region to form a plurality ofopenings in the back passivation layer and the first back surface fieldregion, and forming a second back surface field region at the backsurface of the substrate exposed by the plurality of openings of theback passivation layer and the first back surface field region; forminga first electrode connected to the emitter region; and forming a secondelectrode connected to the first back surface field region and thesecond back surface field region.
 17. The method of claim 16, whereinthe forming of the first back surface field region includes forming amicrocrystalline silicon layer, which is more heavily doped withimpurities of the first conductive type than the substrate, on the backpassivation layer.
 18. The method of claim 17, wherein the forming ofthe first back surface field region further includes forming anamorphous silicon layer containing impurities of the first conductivetype, of which a doping concentration is lower than a dopingconcentration of the microcrystalline silicon layer, on the backpassivation layer before forming the microcrystalline silicon layer. 19.The method of claim 16, further comprising forming a dielectric layer onthe first back surface field region, wherein the laser beam isselectively irradiated onto the dielectric layer.
 20. The method ofclaim 19, wherein a process temperature for forming the dielectric layeris 300° C. to 400° C.